This application claims priority to an application entitled xe2x80x9cMethod of Supporting Power Control on DCCH in BSxe2x80x9d filed in the Korean Industrial Property Office on Apr. 26, 2000 and assigned Ser. No. 2000-22183; the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to an apparatus and method for supporting forward and reverse power control on a DCCH (Dedicated Control Channel) in a BTS (Base station Transceiver System) and a BSC (Base Station Controller).
2. Description of the Related Art
A discontinuous transmission (DTX) mode refers to a mode in which data is transmitted in frames only when transmission data is generated in a wired system or a mobile communication system. Data transmission in the DTX mode minimizes transmission power and increases the whole system capacity due to the decrease of interference with the system.
The DTX, however, exhibits a problem when a receiver does not know whether frames have been transmitted or not because a transmitter transmits frames irregularly. That makes it impossible for a BTS to perform a forward power control. More specifically, when a receiver in a mobile station (MS) cannot make a right judgment about data transmission, it does not rely on decoder decision parameters including CRC (Cyclic Redundancy Code) and decoding results. Hence, the transmission power of the MS cannot be controlled accurately by known methods suitable for a continuous transmission mode.
Both a DCCH and an SCH (Supplemental Channel) support the DTX mode. The DCCH is characterized by data transmission only when transmission data is generated in a higher layer, which makes the DCCH suitable as a control channel for efficient packet services. The DCCH is supposed to transmit null frames for power control during the DTX period. The SCH supports a DTX mode in which no data is transmitted in the absence of transmission data. The SCH transmits no frames during the DTX period.
FIG. 1 is a block diagram of a prior art mobile communication system. The mobile communication system is a reference model of 3G IOS (Interoperability Specifications) with an MSC (Mobile Switching Center), BSs (Base Stations), and a digital air interface between the BSs, which are well known.
Referring to FIG. 1, an interface A1 is defined for signaling and interfaces A2 and A5 (exclusively for circuit data) are defined for user traffic between an MSC 20 and a BSC 32. An interface A3 is defined to connect a target BS 40 to an SDU (Frame Selection/Distribution Unit Function) 34 of a source BS 30 to implement a soft/softer handoff. Signaling messages and user data are transmitted between the target BS 40 and the SDU 34 of the source system 30 by the interface A3. An interface A7 is defined for signal transmission/reception between the target BS 40 and the source BS 30 for inter-BS soft/softer handoff.
The wired communication lines of this CDMA mobile communication system include a forward link directed from the MSC 20 to the BS 30, a reverse link directed from the BS 30 to the MSC 20, and a line between the BSs 30 and 40. The MSC 20 includes a call control and mobility management block 22 and a switching block 24. The MSC 20 is connected to a data network (not shown) such as the Internet through an IWF (InterWorking Function) 50. Interfaces A8 and A9 are defined for user traffic and signaling, respectively between a BS and a PCF (Packet Control Function) 60 and interfaces A10 and A11 are defined for user traffic and signaling, respectively, between the PCF 60 and a PDSN (Packet Data Serving Node) 70.
FIG. 2 is a diagram showing a DCCH signal flow between a BTS and a BSC (BSC-SDU) in conventional CDMA technology. This operation may occur between the BSC 32 (BSC-SDU 34) and a BTS 36 in the source BS 30, or a BSC 42 and a BTS 44 in the target BS 40.
With continued reference to FIG. 2, upon detection of a DTX mode, the BTS determines the type of a data frame to transmit to the BSC and generates a reverse DCCH message in step 11. The reverse DCCH message is supposed to be transmitted to the BSC in every predetermined period (e.g. 20 ms) in response to a reverse DCCH frame received in the predetermined period from an MS (not shown). Step 11 will be described later in more detail with reference to FIGS. 3A and 3B.
In step 12, the BTS transmits the reverse DCCH message to the BSC. The reverse DCCH message may contain a data/null/idle/erasure frame. The BSC receives and processes the reverse DCCH message and generates a forward DCCH message in step 13. Reception of the reverse DCCH message is described below in more detail with reference to FIG. 5; processing the reverse DCCH message and generation of the forward DCCH message is described below with reference to FIGS. 4A and 4B.
In step 14, the BSC transmits the forward DCCH message to the BTS. The forward DCCH message may contain a data/null/idle/erasure frame. The BTS performs a forward/reverse power control for the MS based on power control information included in the forward DCCH message in step 15. Reception of the forward DCCH message is described below in more detail with reference to FIG. 6.
To summarize the operation shown in FIG. 2, after receiving a data frame in every predetermined period (20 ms) from the MS, the BTS generates a reverse DCCH message in the predetermined period and transmits it to the BSC. The BSC processes the reverse DCCH message, generates a forward DCCH message, and transmits it to the BTS. Then, the BTS performs a power control for the MS based on power control information included in the forward DCCH message.
FIGS. 3A and 3B are flowcharts illustrating a conventional reverse DCCH message transmitting operation. In this operation, the BTS transmits a frame received in the predetermined period from the MS as a reverse DCCH message to the BSC-SDU. The following description is conducted with the appreciation that a reverse DCCH message is constructed in the same format as an FCH (Fundamental Channel) message shown in FIGS. 7 and 10, and thus defined as a reverse FCH/DCCH message.
Referring to FIG. 3A, the BTS determines whether it has secured radio resources related with the MS and acquired the MS in step 101. If it has not, the BTS considers that it tries to synchronize with the MS and sets Frame Content in an IS-2000 reverse DCCH message shown in FIG. 10 to an idle frame to synchronize with the BSC-SDU in step 104. Since the BTS is being synchronized with the BSC-SDU, it sets power control information in the reverse FCH/DCCH message that will be transmitted to the BSC-SDU to values negligible to the BSC-SDU in step 106. In step 107, the BTS transmits the IS-2000 reverse FCH/DCCH message to the BSC-SDU.
On the other hand, if the BTS has secured the radio resources related with the MS and acquired the MS in step 101, it checks the quality of a frame received from the MS in step 102. If the data frame is bad, the BTS sets Frame Content of the reverse FCH/DCCH message to an erasure frame in step 104-1. In step 106-1, the BTS sets the power control information of the reverse FCH/DCCH message to values negligible to the BSC-SDU. The BTS transmits the IS-2000 reverse FCH/DCCH message without any data to the BSC-SDU since the received frame is bad in step 107-1. Upon recognition of the erasure frame, the BSC-SDU requests the MS to increase its transmission power regarding reverse power control. That is, since the data frame received from the MS is bad, the BSC-SDU will request the MS to transmit a data frame with incremented power.
If the BTS determines that the received frame is good in step 102, it detects a DTX mode during reception of a reverse DCCH frame from the MS by a known DTX mode detection method applied to a radio transmission period between an MS and a BTS in step 103. If the DTX mode is detected, the BTS goes to step 104-3, otherwise, it goes to step 104-2.
In step 104-2, the BTS sets Frame Content of the reverse FCH/DCCH message to a data frame. The BTS checks whether Frame Content of the latest forward DCCH frame received from the BSC-SDU indicates a null frame in step 105A. If it does not indicate a null frame, the BTS sets information elements related with power control according to the DCCH frame received from the MS in step 106-2.
On the contrary, if the latest forward DCCH frame is a null frame, the BTS sets power control information in the reverse FCH/DCCH message to be negligible to the BSC-SDU in step 106-3. In step 107-2, the BTS transmits the IS-2000 reverse FCH/DCCH message with the data of the 20-ms data frame received from the MS encapsulated to the BSC-SDU. The data received from the MS is filled in Reverse Link Information of the reverse FCH/DCCH message.
Upon detection of a DTX mode in step 103, the BTS sets Frame Content of the reverse FCH/DCCH message to a null frame in step 104-3 in FIG. 3B. In step 105B, the BTS checks whether the latest forward DCCH message is a null frame. If it is not a null frame, the BTS maintains power control information at the DTX mode detected point in the power control information elements of the reverse FCH/DCCH message in step 106-4.
On the other hand, if the latest forward DCCH is a null frame, the BTS sets the power control information of the reverse FCH/DCCH message to be negligible to the BSC-SDU in step 106-5. Since there is no data in the 20-ms frame received from the MS, the BTS transmits the IS-2000 reverse FCH/DCCH message without any data to the BSC-SDU in step 107-3. Here, no data is filled in Reverse Link Information.
FIGS. 4A and 4B are flowcharts illustrating a conventional forward DCCH message transmitting operation. In this operation, the BSC-SDU transmits a forward DCCH message to the BTS in every predetermined period (20 ms). It is to be noted in the following description that a forward DCCH message is constructed in the same format as an FCH shown in FIGS. 7 and 8, and thus defined as a forward FCH/DCCH messages.
Referring to FIG. 4A, the BSC-SDU determines whether it has secured forward radio resources related with the MS and acquired the MS in step 201. If it has not, the BSC-SDU considers that it is being synchronized with the MS and sets Frame Content in an IS-2000 forward FCH/DCCH message of FIG. 8 to an idle frame to synchronize with the BTS in step 203. Since the BSC-SDU is being synchronized with the BTS, it sets power control information in the forward FCH/DCCH message that will be transmitted to the BTS to appropriate values in step 206. Here, forward power control information is set to an initial value for control of the MS and reverse power control information is set based on power control information included in a reverse DCCH message received every 20 ms from the BTS. In step 207, the BSC-SDU transmits the forward DCCH message with the set power control information to the BTS. Here, no data is loaded in the forward DCCH message.
On the other hand, if the BSC-SDU has secured the radio resources related with the MS and acquired the MS in step 201, it checks whether there is data to be transmitted to the MS in the BSC or an external network element (e.g., PDSN) in step 202. If there is no data to transmit to the MS, the BSC-SDU goes to step 203-1 and if there exists data to transmit to the MS, it goes to step 203-2.
In step 203-1, the BSC-SDU sets Frame Content of the forward FCH/DCCH message to a null frame. The BSC-SDU checks whether Frame Content of the latest reverse DCCH frame received from the BTS indicates one of a null frame and an idle frame in step 204A. If it is neither a null frame nor an idle frame, the BSC-SDU checks whether Frame Content of the latest reverse DCCH message indicates an erasure frame in step 205A. If it does not indicate an erasure frame, the BSC-SDU sets power control information in the forward FCH/DCCH message based on power control information included in the reverse DCCH message received from the BTS every 20 ms in step 206-1A. Since there is no data to transmit to the MS, the BSC-SDU loads no data in the forward FCH/DCCH message and transmits it to the BTS in step 207-1.
If Frame Content of the latest reverse DCCH message indicates an erasure frame in step 205A, the BSC-SDU sets a reverse power control information value to indicate power-up on a reverse link in the forward FCH/DCCH message in step 206-2A. Since there exists no data to transmit to the MS, the BSC-SDU transmits the forward FCH/DCCH frame without any data to the BTS in step 207-1.
If Frame Content of the latest reverse DCCH message indicates one of a null frame and an idle frame in step 204A, the BSC-SDU maintains the power control information included in the reverse DCCH message received from the BTS every 20 ms. The power control information is maintained until an erasure frame or a data frame is received from the BTS. That is, the BSC-SDU sets the power control information value to the previous value in the forward FCH DCCH message in step 206-3A. Since there exists no data to transmit to the MS, the BSC-SDU transmits the forward FCH/DCCH frame without any data to the BTS in step 207-1.
If there exists data to transmit to the MS in step 202, the BSC-SDU sets Frame Content of the forward FCH/DCCH to a data frame of 9600 bps or 14400 bps in step 203-2 of FIG. 4B. Then, steps 204B to 207-2 are performed in the same manner as steps 204A to 206-3A. In step 204B, the BSC-SDU checks whether Frame Content of the latest reverse DCCH message is one of a null frame and an idle frame. If it is neither a null frame nor an idle frame, the BSC-SDU checks whether Frame Content of the latest reverse DCCH message indicates an erasure frame in step 205B. If it does not indicate an erasure frame either, it sets the power control information in the forward DCCH message based on power control information included in the reverse DCCH message received from the BTS in step 206-1B. Since there is data to transmit to the MS, the BSC-SDU transmits the forward FCH/DCCH message with the data to the BTS in step 207-2.
If the Frame Content of the latest reverse DCCH message indicates an erasure frame in step 205B, the BSC-SDU sets the reverse power control information value to indicate power-up on the reverse link in the forward DCCH message in step 206-2B. Since there is data to transmit to the MS, the BSC-SDU transmits the forward FCH/DCCH frame with the data to the BTS in step 207-2.
If Frame Content of the latest reverse DCCH message indicates one of a null frame and an idle frame in step 204B, the BSC-SDU maintains the power control information included in the reverse DCCH message received from the BTS every 20 ms. The power control information is maintained until an erasure frame or a data frame is received from the BTS. That is, the BSC-SDU sets the power control information of the forward DCCH message to the previous values in step 206-3B. Since there is data to transmit to the MS, the BSC-SDU transmits the forward FCH/DCCH frame with the data to the BTS in step 207-2.
FIG. 5 is a flowchart illustrating a conventional reverse DCCH message receiving operation. In this operation, the BSC-SDU receives and processes a reverse DCCH message in every predetermined period (e.g., 20 ms) from the BTS.
Referring to FIG. 5, the BSC-SDU receives a reverse FCH/DCCH message from the BTS every 20 ms in step 300. The BSC-SDU determines whether Frame Content of the received message indicates an erasure frame in step 301. If the received frame is an erasure frame, the BSC-SDU goes to step 304, otherwise, it goes to step 302. In the case of an erasure frame, it implies that a frame received at the BTS from the MS is bad. Therefore, the BSC-SDU neglects all information in the received reverse DCCH message and generates a forward FCH/DCCH message indicating reverse power-up in step 304.
If the received reverse DCCH frame is not an erasure frame in step 301, the BSC-SDU determines whether Frame Content of the received frame indicates an idle frame in step 302. In the case of an idle frame, the BSC-SDU neglects all information of the received reverse FCH/DCCH message and generates a forward FCH/DCCH message with reverse power control information maintained at an initial value, considering that the BTS has not recognized the radio resources related with the MS or has not assigned the radio resources in step 304-1.
If the received reverse FCH/DCCH message is not an idle frame in step 302, the BSC-SDU determines whether its Frame Content indicates a null frame in step 303. In the case of a null frame, the BSC-SDU neglects all information of the received reverse FCH/DCCH message and generates a forward DCCH message with reverse power control information maintained at a value set just before a DTX mode is recognized, considering that a reverse channel between the MS and the BTS is in the DTX mode in step 304-2.
If the reverse FCH/DCCH message is not a null frame in step 303, which implies that it is a data frame, the BSC-SDU transmits data included in Reverse Link Information of the reverse FCH/DCCH message to a corresponding data processing device (not shown) according to the type of the data and generates a forward DCCH message with forward/reverse power control information based on an analysis of power control information included in the reverse FCH/DCCH message in step 304-3.
FIG. 6 is a flowchart illustrating a conventional forward FCH/DCCH message receiving operation. In this operation, the BTS receives and processes a forward FCH/DCCH message in every predetermined period (e.g., 20 ms) from the BSC-SDU.
Referring to FIG. 6, the BTS receives a forward FCH/DCCH message from the BSC every 20 ms in step 400. The BTS determines whether Frame Content of the received message indicates an idle frame in step 401. In the case of an idle frame, the BTS analyses all information of the received forward FCH/DCCH message and transmits reverse/forward power control information set in the forward message to a power control processor (not shown) in step 403. Here, no frames are transmitted on a forward radio link.
If the forward FCH/DCCH message is not an idle frame in step 401, the BTS determines whether Frame Content of the forward FCH/DCCH message indicates a null frame in step 402. In the case of a null frame, the BTS analyses all information of the forward FCH/forward DCCH message and transmits reverse/forward power control information set in the forward message to the power control processor in step 403-1. Here, no frames are transmitted on the forward radio link.
If the forward FCH/DCCH message is not a null frame in step 402, which implies that it is a data frame, the BTS analyses all information of the forward FCH/DCCH message and transmits reverse/forward power control information set in the forward message to the power control processor in step 403-2. Here, data included in the channel information of the forward DCCH message is transmitted on the forward radio link.
FIG. 7 illustrates the structure of a message transmitted from the BSC to the BTS on a user traffic sub-channel of an FCH. The message is used to transmit a forward traffic channel frame directed to the MS. This message can be transmitted between a BTS and a BSC in the same BS or between a BTS and a BSC in different BSs although the message is differently called according to the interfaces. For example, the message is called a forward Abis DCCH message in the former case and a forward A3 DCCH message in the latter case.
FIG. 8 illustrates an example Forward Layer 3 FCH/DCCH Data representing control information for a forward CDMA traffic channel frame and a packet directed from an SDU to a target BTS.
FIG. 9 illustrates a message transmitted from the BTS to the BSC on a user traffic sub-channel of an FCH. This message is used for the BTS to transmit a reverse traffic channel frame and control information. The message can be transmitted between a BTS and a BSC in the same BS or between a BTS and a BSC in different BSs although the message is differently called according to the interfaces. For example, the message is called a reverse Abis DCCH message in the former case and a reverse A3 DCCH message in the latter case.
FIG. 10 illustrates an example Reverse Layer 3 FCH/DCCH Data representing control information for a reverse CDMA traffic channel frame and a packet directed from a target BTS to an SDU.
The above-described conventional method produces the following two main disadvantages in a BS.
1. Unstable forward/reverse power control for a DTX period: Since power control information effective at the start point of a DTX mode is maintained for the whole DTX period, an effective power control cannot be performed in reality for the DTX period. Furthermore, power control information for use in power control at the end of the DTX mode reflects no real radio situations, which increases an error rate for a radio transmission period; and
2. Non-supportability for slow power control on forward DCCH: One bit for slow power control, namely an EIB (Erasure Indicator Bit) for an FCH is transmitted in every 20-ms frame in the conventional technology. Because a DCCH supports a DTX mode, the EIB for the FCH is not effective in slow power control. Therefore, slow forward power control should be performed on the DCCH by supporting a QIB (Quality Indicator Bit) that works well in both a DTX mode and a non-DTX mode. Here, the EIB is one bit of power control information for an FCH in a 20-ms frame and the QIB is one bit of power control information for a DCCH in a 20-ms frame.
It is, therefore, an object of the present invention to provide an apparatus and method for effectively supporting power control on a forward/reverse DCCH for a DTX period in a CDMA mobile communication system.
It is another object of the present invention to provide an apparatus and method for performing slow power control on a DCCH by use of a QIB in a CDMA mobile communication system.
The foregoing and other objects are achieved by a method of supporting power control on a DCCH in a BS. According to one aspect of the present invention, a BTS receives forward power control (FPC) mode information indicating a low power control from the BSC and transmits the FPC mode information to an MS. Then, the BTS extracts a QIB that is a power control command in a frame period from a reverse pilot channel received from the MS according to the FPC mode information and determines the status of the QIB. The BTS transmits information requesting the BSC to change a threshold for a power control on a forward DCCH based on the determined QIB status to the BSC.
According to another aspect of the present invention, a BTS detects a DTX period by measuring the energy of a DCCH data frame received from an MS, determines reception status by measuring the energy of a PCB on a reverse pilot channel if the DTX mode is detected, determines FQI (Frame Quality Indicator) information according to the determined reception status, and transmits the FQI information to a BSC.